The present invention relates to implants having a porous surface. More specifically it relates to implants having a porous surface wherein the implants are made by attaching the implant body to the porous surface by molding.
Increasingly, attention is being focused on the use of nonmetallic materials for constructing prosthetic orthopaedic implants. Materials such as thermoplastics, thermoplastic composites, ceramics, and others have been used to better match the flexural rigidity of bone and eliminate patient exposure to metal ions. These materials are often also advantageously shaped by economical molding processes such as injection molding or compression molding. As with implants constructed of other materials it is desirable to provide a porous surface on the implant surface to accommodate bone ingrowth or cement interdigitation. Typically the porous surface comprises a wire mesh or beaded or dimpled surface.
U.S. Pat. Nos. 4,978,355, 4,955,911, 4,813,960 and UK Patent Application GB 2 216 425 A teach providing a porous surface on a plastic implant by pressing a heated wire mesh into the plastic implant body. U.S. Pat. No. 4,955,911 and GB 2 216 425 A teach a permanent solid layer within the wire mesh to prevent the outer pores of the mesh from becoming filled with plastic. U.S. Pat. No. 4,778,469 teaches forming a textured surface on a plastic implant by pressing a heated, textured plate into the implant surface and then dissolving the plate to leave behind the impression of the plate. Finally, U.S. Pat. No. 4,479,271 teaches molding a plastic implant to a wire mesh.